Drive for a symmetrical bipolar transistor

ABSTRACT

A drive circuit for triggering a symmetrical bipolar transistor, the drive circuit having a balanced circuit connected to two operating electrodes of the symmetrical bipolar transistor. The balanced circuit includes two parts connected by their bases. Collectors of the two parts of the balanced circuit act on inverse balanced circuits which control a switching device which in turn controls the triggering of the symmetrical bipolar transistor.

BACKGROUND OF THE INVENTION

Symmetrical bipolar transistors have many applications. In a knownapplication, a bipolar transistor is used as a reverse-polarityprotection element in a coupling circuit to a bus system. (See EuropeanPatent Publication No. EP-A-0487 759, FIG. 3.) Such reverse-polarityprotection is preferably suitable for assemblies in bus systems, incomputers and in controllers with a storage capability. Thereverse-polarity protection element is located in a signal coupling pathand serves as a controllable element which switches the signal couplingpath on and off as a function of the polarity of an electrical signal.The known bipolar transistor is designed as a double-emitter transistorwhose emitter current can be controlled uniformly in both directions.

A bipolar transistor structure is also generally suitable for checkingwhether a potential difference is less than a specific value and thus,in addition, whether a voltage is approaching another voltage. Untilnow, comparators have been used for such applications. The requiredcomparator arrangements are normally rather complex, however. A nationalGerman application having an older priority (German Patent ApplicationNo. DE-A-43 16 608) discusses a bipolar transistor structure.

If a bipolar transistor structure is intended to be integrated in anintegrated circuit, it is desirable to minimize the power losses whichoccur and to keep the currents for driving such bipolar transistorstructures correspondingly low. The object of the present invention isto find a driver circuit for a symmetrical bipolar transistor and for abipolar transistor structure in an IC circuit, which operates with drivecurrents which are as low as possible.

SUMMARY OF THE INVENTION

The above mentioned object is achieved by providing an improved drivercircuit for controlling a symmetrical bipolar transistor, or forcontrolling a symmetrical bipolar transistor structure, having twooperating electrodes. The driver circuit includes a pair of balancedcircuits, a pair of inverse balanced circuits and a switch. The pair ofbalanced circuits is coupled with the two operating electrodes, arecoupled to one another by their bases, and have a reference currentsupplied to their bases. The pair of inverse balanced circuits are actedupon by collectors of the pair of balanced circuits. The switch iscontrolled by the pair of inverse balanced circuits and has an openstate and a closed state in which a triggering current flows to the baseof the symmetrical bipolar transistor. The switch is in the open statewhen the two operating electrodes of the symmetrical bipolar transistorare at the same potential.

A balanced circuit of a type which is known per se is connected to thetwo operating electrodes of the symmetrical bipolar transistor or of thesymmetrical bipolar transistor structure. The balanced circuit canpreferably be connected with the operating electrode by means of itsemitter. In this case, the bases of the two balanced circuits areconnected to one another, and the collectors of the two balancedcircuits act on inverse balanced circuits. The inverse balanced circuitsregulate the control current required to control the bipolar transistor.In such an arrangement, using low drive currents for the symmetricalbipolar transistor or the symmetrical bipolar transistor structure ispossible. Both arrangements are called bipolar transistors, for short,in the following text.

The balanced circuits can each be extended, as first balanced circuits,by a second amplifying balanced circuit. The second balanced circuitsare each connected to a collector of the first balanced circuit. Such anarrangement permits current pulses having a very high edge gradient tobe sent via the bipolar transistor.

In a preferred embodiment of the present invention, the second,amplifying balanced circuits are connected, via coupled ENABLE switches,to the first balanced circuits. In each case, the collectors of thefirst balanced circuits in this case act on one amplifying balancedcircuit via the ENABLE switches. One amplifying balanced circuit is, ineach case, connected directly to a collector of a first balancedcircuit, possibly with the intermediate connection of an ENABLE switch.Such a driver circuit operates at very high speed, with a control delayof only a few hundred ns. As a result of the increased currentconsumption, it is, however, favorable to connect the amplifyingbalanced circuits via the ENABLE switches only in the case oftransmission.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is now intended to be explained in more detail withreference to exemplary embodiments which are illustrated in the drawing.

FIG. 1 is a schematic which shows a bipolar transistor driven by adriver circuit having a balanced circuit and a downstream inversebalanced circuit.

FIG. 2 is a schematic which shows a bipolar transistor driven by adriver circuit having two sets of balanced circuits according to FIG. 1and, in each case, one amplifying second balanced circuit.

FIG. 3 is a schematic which shows another circuit diagram for anindividual balanced circuit arrangement.

FIG. 4 is a schematic which shows the classic illustration of aDARLINGTON circuit for transistors.

DETAILED DESCRIPTION

The bipolar transistor 1 according to FIG. 1 is designed as adouble-emitter transistor. It is connected in a line 2 of a conductorarrangement, composed of the lines 2 and 3, by means of its operatingelectrodes, the emitter electrodes. One connection 4 leads to the baseof the bipolar transistor. First balanced circuits 5 and 6 are, in eachcase, connected to the emitters of the bipolar transistor 1. The basesof these balanced circuits 5 and 6 are connected to one another. Onecollector 11, 11', in each case, of the first balanced circuits 5 and 6,respectively, controls an inverse balanced circuit 7 or 8, respectively.The resistors 9, 9' and, if required, the resistors 10, 10' may beprovided to modify the transmission characteristics, in the case of anadjustable mirror characteristic, such as those provided based on the ICsurfaces of the balanced circuits.

The outputs of the inverse balanced circuits are connected to aresistors 12, 12'. The resistors 12, 12' are supplied from aconstant-voltage source 13 with respect to ground. The outputs of theinverse balanced circuits 7 and 8 furthermore act on, in each case, onebase of a transistor 14, 14' for example in a DARLINGTON circuit. Thetransistors 14, 14' are connected by means of their collectors to thebase as the control electrode of the bipolar transistor 1. The resistors15 and 16 are used for linearizing and current limiting.

In the design according to FIG. 2, second amplifying balanced circuits17 and 18 are, in each case, connected, via ENABLE switches 19, 19', inprinciple to a circuit arrangement according to FIG. 1. The ENABLEswitches 19, 19' are, in each case, connected to a further collector ofthe first balanced circuit 5 or 6, respectively. A reference voltage isconnected again as a constant voltage source 13, and a reference currentsource 20 again supplies the first balanced circuits 5 and 6.

The circuit according to FIG. 1 operates as follows:

The excitation current 20 from a constant current source is splitbetween the balanced circuit formed by the first balanced circuits 5 and6, depending on whether the operating electrode 21 or the operatingelectrode 22 of the bipolar transistor 1 is at a more positivepotential. If the potential on the operating electrode 21 is morepositive than that on the operating electrode 22, then the firstbalanced circuit 5 draws more current than the other first balancedcircuit 6. However, if the potential on the operating electrode 22 ismore positive than that on the operating electrode 21, then the firstbalanced circuit 6 draws more current that the other first balancedcircuit 5.

If the bipolar transistor 1 is fully saturated, in which case thepotentials on the operating electrodes 21 and 22 are equal, theexcitation current 20 is split uniformly between the first balancedcircuits 5 and 6. The balanced circuit is then in balance. In this case,the two inverse balanced circuits 7 and 8 draw the same current. Theresistors 12, 12' are dimensioned such that the same voltage drop occurson each in the indicated state. This voltage drop corresponds to, or isequal to, the voltage from the constant voltage source 13. As aconsequence, the bases of the transistors 14, 14', which are shown inthe exemplary embodiment as DARLINGTON transistors, are effectivelyconnected to ground (or 0 V). Accordingly, no current can flow in thecollectors of the transistors 14, 14' from the control electrode of thebipolar transistor 1, via the connection 4.

The drive current does not rise until the balance formed by the firstbalanced circuits 5 and 6 is no longer in balance. The operatingelectrode 21 or 22 becomes more negative depending on the direction of acurrent via the bipolar transistor 1, so that one of the two transistors14, 14' receives a positive drive and, as a consequence, supplies therequired drive current to the bipolar transistor 1.

In the circuit arrangement according to FIG. 2, the collectors of thefirst balanced circuits 5 and 6 respectively, which are passed viaENABLE switches 19, 19', act on, in each case, one amplifying balancedcircuit 17 or 18, respectively. This additional drive operates at a veryhigh speed, with a control delay of a few hundred ns, for example. Thefact that the amplifying second balanced circuits 17 and 18intrinsically have a greater current consumption can be corrected by theENABLE switches 19, 19'. It is favorable to carry out the connection viathe ENABLE switches 19, 19' only in the event of transmission.

FIG. 3 shows another illustration of the first balanced circuits 5 and 6respectively. This illustration was more common in the past. FIG. 4shows a classic illustration of the transistors 14, 14' which are shownin FIG. 1, for example, as DARLINGTON transistors.

I claim:
 1. A driver circuit for controlling a symmetrical bipolartransistor, or for controlling a symmetrical bipolar transistorstructure, having two operating electrodes, the driver circuitcomprising:a) a pair of balanced circuits coupled with the two operatingelectrodes, the pair of balanced circuits being coupled to one anotherby their bases and having a reference current supplied to their bases;b) a pair of inverse balanced circuits, the pair of inverse balancedcircuits being acted upon by collectors of the pair of balancedcircuits; and c) a switch, the switch being driven by the pair ofinverse balanced circuits and having an open state and a closed state inwhich a triggering current flows to the base of the symmetrical bipolartransistor, wherein the switch is in the open state when the twooperating electrodes of the symmetrical bipolar transistor are at thesame potential.
 2. The drive circuit of claim 1 further comprising apair of amplifying balanced circuits, each of the pair of amplifyingbalanced circuits being coupled with a further collector of a respectiveone of the pair of balanced circuits.
 3. The drive circuit of claim 2wherein the pair of amplifying balanced circuits are coupled, via enableswitches, to the balanced circuits.
 4. A circuit for triggering asymmetrical bipolar transistor having two operating electrodes and abase electrode, the circuit comprising:a) a first balanced circuit, thefirst balanced circuit havingi) a first part having an emitter coupledwith one of the two operating electrodes of the symmetrical bipolartransistor, a base, and at least one collector, and ii) a second parthaving an emitter coupled with an other of the two operating electrodesof the symmetrical bipolar transistor, a base coupled with the base ofthe first part of the first balanced circuit and coupled with areference current source, and at least one collector; b) an inversebalanced circuit, the inverse balanced circuit havingi) a first parthaving a control input coupled with one of the at least one collector ofthe first part of the first balanced circuit and having an output, andii) a second part having a control input coupled with one of the atleast one collector of the second part of the first balanced circuit andhaving an output; and c) a switching device for controllably switchingthrough a triggering current to the base of the symmetrical bipolartransistor, the switching device havingi) a first part having an emittercoupled with a triggering current source, a collector coupled with thebase of the symmetrical bipolar transistor, and a base coupled with theoutput of the first part of the inverse balanced circuit and coupledwith a reference voltage, and ii) a second part having an emittercoupled with a triggering current source, a collector coupled with thebase of the symmetrical bipolar transistor, and a base coupled with theoutput of the second part of the inverse balanced circuit and coupledwith the referenced voltage, whereby, the first and second parts of theswitching device remain open when the two operating electrodes of thesymmetrical bipolar transistor are at the same potential.
 5. The circuitof claim 4 further comprising:d) an amplifying balanced circuit havingi)a first part having an input coupled with another of the at least onecollector of the first part of the first balanced circuit, and having anoutput coupled with the base of the symmetrical bipolar transistor, andii) a second part having an input coupled with another of the at leastone collector of the second part of the first balanced circuit, andhaving an output coupled with the base of the symmetrical bipolartransistor.
 6. The circuit of claim 5 further comprising:e) an enableswitch arranged between the another of the at least one collector of thefirst part of the first balanced circuit and the input of the first partof the amplifying balanced circuit; and f) an enable switch arrangedbetween the another of the at least one collector of the second part ofthe first balanced circuit and the input of the second part of theamplifying balanced circuit.